The present invention relates to a method and an arrangement for, in connection with an external fire in an ammunition bunker, preventing ammunition components stored therein, and then perhaps chiefly rocket engines, from exploding. The invention is based on, in the quantity of explosive enclosed in each ammunition component, before the explosive has reached its ignition temperature as a result of external heating but during the gradual decomposition of the explosive during heating, allowing combustion gases formed in this connection access to a free gas outlet of sufficient cross-sectional area in order to prevent the heating resulting in an explosion. The object of the invention is therefore to limit the damage caused by a fire in the event of external heating of the products concerned here.
The state of the art includes a number of various different proposals with regard to how rocket engines could be prevented from exploding in the event of external fire in, for example, the ammunition bunker where they are stored awaiting use. Several of these earlier proposals are based on making the outer casing of the rocket engines of at least partly temperature-sensitive or fire-sensitive material which, in the event of external fire, will be capable of, from the outside, being weakened sufficiently or being burnt through completely before the propellent powder of the rocket engine has reached its critical ignition temperature. In these older methods as well, the intention is therefore to limit the damage caused by a fire by making sufficient gas outlets available when the gas pressure inside the engine rises to such a great extent that an explosion would otherwise result.
Variants on this subject are described in U.S. Pat. Nos. 4,084,512, 4,442,666 and 4,458,482.
SE-A2-508,650 also describes a method and an arrangement for, with the same intention, preventing an external fire in an ammunition bunker containing fixed artillery ammunition with a charge consisting of what is known as LOVA powder giving rise to an explosion. The burning rate of the LOVA powder is heavily pressure-dependent and, according to this earlier proposal, the cases of the fixed ammunition were therefore provided with weakenings which, when fired in the weapon concerned, cope with the barrel pressure as long as they are supported by the chamber of the weapon but, if they do not have the support of the chamber, break and split open when the internal gas pressure rises above a predetermined value.
The invention concerned here therefore relates to an attempt to solve a previously known problem in a radical new manner. Instead of making use of fire-sensitive outer material in the cases or equivalent enclosing the explosive or of providing the same cases with weakenings made beforehand, we are now proposing making the cases enclosing the explosive in a number of separate parts and assembling these case parts purely mechanically with inserts or mounting components which are made from what are known as shape memory alloys. These inserts or mounting components are also to have such properties that, at a preselected temperature which lies well below the temperature when an explosion is imminent, they eliminate the interconnection between the case parts concerned so that the gas formation which precedes an explosion has a free outlet. In order for this basic principle to be capable of functioning, it is necessary that it is not possible for the mounting components made of shape memory alloy to be heated to their own critical temperature during the burning time of the rocket engine as they will then initiate the safety function built into the invention.